1. Field of the Disclosure
This disclosure relates to a backlight unit, and more particularly to a backlight unit with advantages of being thin and of reducing manufacturing time, and a liquid crystal display (LCD) device with the same.
2. Description of the Related Art
Cathode ray tubes (CRTs) correspond to one of display devices which are widely used. The CRTs are mainly used as monitors for TVs, measuring apparatuses, or information terminals. However, the heavy weight and large size of the CRTs have been a major hindrance to the manufacturing of small, light electronic products.
In other words, the CRTs have the limitations of weight and size in the current trend of small, light electronic products. Under such circumstances, LCD devices using an electro-optical effect, plasma display panels (PDPs) using a gas discharge, electro luminescence display devices using a electro-luminescent effect, and so on are expected to substitute for CRTs.
Among the substitutable display devices, LCD devices are being actively researched. Also, LCD devices are gradually being used in a wide range of applications due to their advantages such as lightness, thinness, and low power consumption. Moreover, LCD devices are being manufactured to have even larger screens, be thinner, and consume less power, in order to meet the requirements of users. Such LCD devices display images by controlling the amount of light transmitted through liquid crystal.
The LCD devices are not self-illuminating display devices, unlike CRTs. As such, an LCD device includes a backlight unit provided on the rear surface of an LCD panel. The backlight unit includes a separated light source providing the light necessary to display an image. The backlight unit can be classified as either an edge type or a direct type in accordance with the disposition of a light source.
Such an edge type backlight unit is mainly applied to comparatively small-sized LCD devices such as the monitors of laptops and desk-top computers. The edge type backlight unit has good light uniformity, a lengthened lifespan, and the advantage of thinning the LCD device.
The direct type backlight unit has begun to be concentrically developed as the LCD device is enlarged to a size above 20 inches. The direct type backlight unit forces light to be directly irradiated onto the entire surface of the LCD panel. To this end, the direct type backlight unit includes a plurality of light sources arranged on the lower surface of a diffusion plate. Since the direct type backlight unit has a higher light efficiency than the edge type backlight unit, it is mainly used for LCD devices of a large size which require a high brightness.
The backlight unit employs a plasma type light source, such as a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL), an external electrode fluorescent lamp (EEFL), an external and internal electrode fluorescent lamp (EIFL), or others, as a light source. Alternatively, the backlight unit uses a white light emission diode (LED) as a light source. Particularly, the white LED is widely used in the backlight unit because of its features of long lifespan, low power consumption, small size, durability, and others.
The edge type backlight unit with the LEDs is configured to include a printed circuit board (PCB) disposed at an inner side surface of a box-shaped bottom cover with an opened upper surface. The LEDs are arranged at fixed intervals on the PCB. More specifically, the LEDs are loaded on respective pad portions, respectively. The pad portions loaded with the LEDs are arranged on the PCB in such a manner as to form one row line.
Such a PCB included in the related art backlight unit is configured to include wirings which transfer driving signals to electrodes of the LEDs. The wirings are formed along a longitude direction of the PCB. As such, the PCB is necessary to have regions, which each have an enough width for the formation of the wirings, adjacent to the top and bottom edges of the row of pads.
Moreover, the LEDs can be driven in such a manner as to be divided into a plurality of channels. In this case, the wirings become more complex, and furthermore the width of the PCB being an important factor in the thickness of the backlight unit becomes larger. Therefore, it is difficult to manufacture a thinner backlight unit.
The PCB included in the related art backlight unit can be formed to have at least two layers, in order to arrange the row of pad portions and the wirings on different layers. As such, the width of the PCB can be reduced. However, at least one manufacturing process is added, manufacturing costs largely increase, and heat radiating effect is deteriorated.